Pink diamonds captivate sensor researchers

TAKASHI KUROKAWA, Nikkei staff writer

TOKYO -- Jewelry aficionados are not the only ones in love with pink diamonds. Researchers in the field of semiconductors and telecommunications are also fascinated by the gemstone for its potential ability to measure temperatures and detect trace amounts of electromagnetic radiation emitted from even a tiny area.

Professor Hiroshi Kawarada of Waseda University uses a model of diamond crystals to investigate NV centers.

The use of pink diamonds could, for example, lead to smaller versions of the massive MRI machines currently used for medical diagnosis. Japanese researchers are conducting advanced basic research into the gemstone, while those in Western countries are focusing more on applications.

Helpful impurities

Diamond crystals usually consist solely of carbon atoms. When nitrogen impurities are present, holes in the crystal created by missing carbon atoms combine with the nitrogen atoms to form a structure known as a nitrogen-vacancy center. When sunlight reaches an NV center inside the diamond, it emits red fluorescence, which makes the stone look pink.

The NV center is negatively charged and exhibits a property known as electron spin. It has been shown, both theoretically and experimentally, that the fluorescence intensity changes when an NV center is exposed to both light and magnetism at the same time. This property of pink diamonds is expected to help in detecting localized magnetic fields.

The Japan Science and Technology Agency, a government research body, is working to develop a new type of biomagnetism measuring system using pink diamonds. Mutsuko Hatano, a professor at the Tokyo Institute of Technology, is leading the project, which began in October 2013 and is slated to be completed by March 2019.

"We aim to develop a handheld MRI that can be used in a variety of applications, from medical checkups to measuring glucose in food," Hatano said.

Five other universities, as well as the National Institute of Advanced Industrial Science and Technology are taking part in the project, and semiconductor maker Renesas Electronics plans to promote the research for developing commercial applications. The goal is to develop highly sensitive magnetic sensors with a resolution capability of several microns, about 100 times more powerful than current sensors. By applying complementary metal-oxide semiconductors, widely used for imaging in cameras, the sensor will be able to detect magnetism at room temperature.

Government support needed

A publicly funded project to study NV centers was launched in June 2014. Hiroshi Kawarada, a professor at Waseda University, is leading the five-year project with other members, including the University of Tsukuba and the Japan Atomic Energy Agency. "Our study aims to understand the magnetism of individual biomolecules," Kawarada said. "We will examine in detail how DNA and proteins interact inside the body, which will help to advance the fields of biology, medicine and pharmaceutical science."

Japanese telecom giant Nippon Telegraph and Telephone is also exploring new areas of application for the technology. The company aims to promote the development of high-speed quantum computers using electron spin properties. According to Kawarada, the potential market for sensors and quantum computers is immeasurable. He said more government-led efforts are needed, pointing out that in terms of applied research into NV centers, Japan is far behind Western countries.